Generation, transmission and rendering of virtual reality multimedia

ABSTRACT

A method of generating virtual reality data includes: obtaining point cloud data, the point cloud data including colour and three-dimensional position data for each of a plurality of points corresponding to locations in a capture volume; generating primary image data containing (i) a first projection of a first subset of the points into a two-dimensional frame of reference, and (ii) for each point of the first subset, depth data derived from the corresponding position data; generating secondary image data containing (i) a second projection of a second subset of the points into the two-dimensional frame of reference, the second projection overlapping with at least part of the first projection in the two-dimensional frame of reference, and (ii) for each point of the second subset, depth data derived from the corresponding position data; and storing the primary image data and the secondary image data in a memory.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from PCT patent application no. PCT/CA2015/000306, filed May 13, 2015 and entitled “Method, System And Apparatus For Generation And Playback Of Virtual Reality Multimedia”, which is incorporated herein by reference.

FIELD

The specification relates generally to processing techniques for multimedia data, and specifically to the generation, transmission and rendering of virtual reality multimedia.

BACKGROUND

Virtual reality display devices, such as the GearVR and the Oculus Rift, enable viewing of content such as video, games and the like in a virtual reality environment, in which the display adapts to the user's movements. Various challenges confront implementations of virtual reality display. For example, particularly in the case of captured video, capturing video from a sufficient variety of viewpoints to account for potential movements of the operator of the display can be difficult, particularly for large or complex scenes. In addition, the resulting volume of captured data can be large enough to render storing, transmitting and processing the data prohibitively costly in terms of computational resources.

SUMMARY

According to an aspect of the specification, a method of generating virtual reality multimedia data is provided, comprising: obtaining point cloud data at a processor of a generation computing device, the point cloud data including colour and three-dimensional position data for each of a plurality of points corresponding to locations in a capture volume; generating, at the processor, primary image data containing (i) a first projection of a first subset of the points into a two-dimensional frame of reference, and (ii) for each point of the first subset, depth data derived from the corresponding position data; generating, at the processor, secondary image data containing (i) a second projection of a second subset of the points into the two-dimensional frame of reference, the second projection overlapping with at least part of the first projection in the two-dimensional frame of reference, and (ii) for each point of the second subset, depth data derived from the corresponding position data; and storing the primary image data and the secondary image data in a memory connected to the processor.

BRIEF DESCRIPTIONS OF THE DRAWINGS

Embodiments are described with reference to the following figures, in which:

FIG. 1 depicts a system for generating, transmitting and rendering virtual reality multimedia data, according to a non-limiting embodiment;

FIG. 2 depicts a method of generating, transmitting and rendering virtual reality multimedia data, according to a non-limiting embodiment;

FIGS. 3A and 3B depict a capture volume and point cloud data generated by the method of FIG. 2, according to a non-limiting embodiment;

FIG. 4 depicts example capture apparatuses of the system of FIG. 1, according to a non-limiting embodiment;

FIG. 5 depicts a method of obtaining point cloud data, according to a non-limiting embodiment;

FIG. 6 depicts a method of generating primary and secondary image data, according to a non-limiting embodiment;

FIGS. 7A and 7B depict an implementation of cube mapping in the method of FIG. 2, according to a non-limiting embodiment;

FIG. 8 depicts primary image data generated by the method of FIG. 2, according to a non-limiting embodiment;

FIGS. 9A and 9B depict secondary image data generated by the method of FIG. 2, according to a non-limiting embodiment;

FIGS. 10A and 10B depict secondary image data generated by the method of FIG. 2, according to another non-limiting embodiment;

FIG. 11 depicts an example data structure for the secondary image data, according to a non-limiting embodiment;

FIG. 12 depicts a method of generating index data at a generation device, according to a non-limiting embodiment;

FIG. 13A and 13B depict an example performance of blocks 1210 and 1215 of the method of FIG. 12, according to a non-limiting embodiment; and

FIG. 14 depicts a rendering index generated at the generation device of FIG. 1, according to a non-limiting embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 1 depicts a system 100 for generation, transmission and rendering of virtual reality multimedia data. In the examples discussed herein, the multimedia data includes image data, and preferably video data (i.e. sequences of images). The video data can be accompanied by audio data, but the generation and subsequent processing of audio data is not of particular relevance to the present disclosure, and is therefore not discussed in further detail. As will become apparent throughout the discussions below, the virtual reality multimedia data herein is distinguished from conventional two-dimensional image or video data in that the virtual reality multimedia data simulates the physical presence of a viewer within the volume (also referred to as a scene) depicted by the multimedia data. Thus, for example, movement of the viewer's head can be tracked and used to update the appearance of the multimedia data to simulate three-dimensional movement of the viewer within the depicted volume.

System 100 includes a generation computing device 104, also referred to herein as generation device 104. Generation device 104, as will be discussed in detail below, is configured to generate the above-mentioned virtual reality multimedia data for transmission to, and rendering at, a client computing device 108, also referred to herein as client device 108. Client device 108 is configured to receive the virtual reality multimedia data generated by generation device 104, and to render (that is, play back) the virtual reality multimedia data. The virtual reality multimedia data can be transferred between generation device 104 and client device 108 in a variety of ways. For example, the multimedia data can be transmitted to client device 108 via a network 112. Network 112 can include any suitable combination of wired and wireless networks, including but not limited to a Wide Area Network (WAN) such as the Internet, a Local Area Network (LAN) such as a corporate data network, cell phone networks, WiFi networks, WiMax networks and the like.

Transmission of the multimedia data to client device 108 via network 112 need not occur directly from generation device 104. For example, the multimedia data can be transmitted from generation device 104 to an intermediate device via network 112, and subsequently to client device 108. In other embodiments, the multimedia data can be sent from generation device 104 to a portable storage medium (e.g. optical discs, flash storage and the like), and the storage medium can be physically transported to client device 108.

Generation device 104 can be based on any suitable computing environment, such as a server or personal computer. In the present example, generation device 104 is a desktop computer housing one or more processors, referred to generically as a processor 116. The nature of processor 116 is not particularly limited. For example, processor 116 can include one or more general purpose central processing units (CPUs), and can also include one or more graphics processing units (GPUs). The performance of the various processing tasks discussed herein can be shared between such CPUs and GPUs, as will be apparent to a person skilled in the art.

Processor 116 is interconnected with a non-transitory computer readable storage medium such as a memory 120. Memory 120 can be any suitable combination of volatile (e.g. Random Access Memory (“RAM”)) and non-volatile (e.g. read only memory (“ROM”), Electrically Erasable Programmable Read Only Memory (“EEPROM”), flash memory, magnetic computer storage device, or optical disc) memory. In the present example, memory 120 includes both a volatile memory and a non-volatile memory. Processor 116 and memory 120 are generally comprised of one or more integrated circuits (ICs), and can have a wide variety of structures, as will now be apparent to those skilled in the art.

Generation device 104 can also include one or more input devices 124 interconnected with processor 116. Input device 124 can include any suitable combination of a keyboard, a mouse, a microphone, and the like. Such input devices are configured to receive input and provide data representative of such input to processor 116. For example, a keyboard can receive input from a user in the form of the depression of one or more keys, and provide data identifying the depressed key or keys to processor 116.

Generation device 104 can also include one or more output devices interconnected with processor 116, such as a display 128 (e.g. a Liquid Crystal Display (LCD), a plasma display, an Organic Light Emitting Diode (OLED) display, a Cathode Ray Tube (CRT) display). Other output devices, such as speakers (not shown), can also be present. Processor 116 is configured to control display 128 to present images to an operator of generation device 104. Generation device 104 also includes one or more network interfaces interconnected with processor 116, such as a network interface 132, which allows generation device 104 to connect to other computing devices (e.g. client device 108) via network 112. Network interface 132 thus includes the necessary hardware (e.g. radios, network interface controllers, and the like) to communicate over network 112.

As noted above, generation device 104 is configured to generate the multimedia data to be provided to client device 108. To that end, generation device is connected to, or houses, or both, one or more sources of data to be employed in the generation of virtual reality multimedia data. The sources of such raw data can include a multimedia capture apparatus 134. In general, capture apparatus 134 captures video (with or without accompanying audio) of an environment or scene and provides the captured data to generation device 104. Capture apparatus 134 will be described below in greater detail. The sources of raw data can also include, in some embodiments, an animation application 135 (e.g. a three-dimensional animation application) stored in memory 120 and executable by processor 116 to create the raw data. In other words, the virtual reality multimedia data can be generated from raw data depicting a virtual scene (via application 135) or from raw data depicting a real scene (via capture apparatus 134).

Client device 108 can be based on any suitable computing environment, such as a personal computer (e.g. a desktop or laptop computer), a mobile device such as a smartphone, a tablet computer, and the like. Client device 108 includes a processor 136 interconnected with a memory 140. Client device 108 can also include an input device 144, a display 148 and a network interface 152. Processor 136, memory 140, input device 144, display 148 and network interface 152 can be substantially as described above in connection with the corresponding components of generation device 108. As will be discussed in greater detail below, in some embodiments the components of client device 108, although functionally similar to those of generation device 104, may have limited computational resources relative to generation device 104. For example, processor 136 can include a CPU and a GPU that, due to power, thermal envelope or physical size constraints (or a combination thereof), are able to process a smaller volume of data in a given time period than the corresponding components of generation device 104. As noted in connection with generation device 104, the CPU and GPU of client device 108 (collectively referred to as processor 136) can share computational tasks between them, as will be apparent to those skilled in the art. In certain situations, however, as will be described below, specific computational tasks are assigned specifically to one or the other of the CPU and the GPU.

In addition, system 100 includes a virtual reality display 156 connected to processor 136 of client device 108 via any suitable interface. Virtual reality display 156 includes any suitable device comprising at least one display and a mechanism to track movements of an operator. For example, virtual reality display 156 can be a head-mounted display device with head tracking, such as the Oculus Rift from Oculus VR, Inc. or the Gear VR from Samsung. Virtual reality display 156 can include a processor, memory, communication interfaces, displays and the like beyond those of client device 108, in some embodiments. In other embodiments, certain components of client device 108 can act as corresponding components for virtual reality display 156. For example, the above-mentioned Gear VR device mounts a mobile device such as a smart phone, and employs the display (e.g. display 148) and processor (e.g. processor 136) of the smart phone. In any event, client device 108 is configured to control virtual reality display 156 to render the virtual reality multimedia received from generation device 104.

In general, generation device 104 is configured, via the execution by processor 116 of a virtual reality data generation application 160 consisting of computer readable instructions maintained in memory 120, to receive source data (also referred to as raw data) from capture apparatus 134 or application 135 (or a combination thereof), and to process the source data to generate virtual reality multimedia data packaged for transmission to client device 108. Client device 108, in turn, is configured via the execution by processor 136 of a virtual reality playback application 164 consisting of computer readable instructions maintained in memory 140, to receive the virtual reality multimedia data generated by generation device 104, and process the virtual reality multimedia data to render a virtual reality scene via virtual reality display 156. Those skilled in the art will appreciate that in some embodiments, the functionality of the above-described applications (e.g. applications 135, 160 and 164) may be implemented using pre-programmed hardware or firmware elements (e.g., application specific integrated circuits (ASICs), electrically erasable programmable read-only memories (EEPROMs), etc.), or other related components.

Turning now to FIG. 2, the generation, transmission and rendering of multimedia data mentioned above will be described in further detail in connection with a method 200. Method 200 will be described in conjunction with its performance in system 100; specifically, certain blocks of method 200 are performed by generation device 104, while other blocks of method 200 are performed by client device 108, as illustrated. It is contemplated that method 200 can also be performed by other suitable systems.

Beginning at block 205, generation device 104 is configured to obtain point cloud data. The point cloud data includes colour and three-dimensional position data for each of a plurality of points corresponding to locations in a capture volume. An example illustration of point cloud data obtained at block 205 is shown in FIGS. 3A and 3B. FIG. 3A depicts an object 300 in a capture volume 304 to be represented in virtual reality multimedia data. FIG. 3B depicts point cloud data 306 representing capture volume 304. That is, the outer boundaries of point cloud data 306 reflect the outer boundaries of capture volume 304, such that point cloud data 306 can represent any object within capture volume 304. As seen in FIG. 3B, object 300 is represented in point cloud data 306 by a plurality of points 308 (two of which are labelled). More generally, any object visible within capture volume 304 is depicted in point cloud data 306; the only points visible in point cloud data 306 are those defining object 300, because for illustrative purposes it has been assumed that object 300 is the only object present within capture volume 304.

As noted above, each point 308 in point cloud data 306 includes colour data and three-dimensional position data. The colour data indicates the colour of the point 308 in any suitable representation of any suitable colour model (e.g. RGB, CMYK, HSV, HSL, YUV and the like). The position data indicates the position of the point 308 within point cloud 306, and thus corresponds to a certain location in capture volume 304. The nature of the position data is also not particularly limited. For example, the position data can be in the form of a set of Cartesian coordinates (e.g. distances along x, y, and z axes that intersect at the center of point cloud data 306). In another example, the position data can be in the form of spherical coordinates (e.g. a radial distance, a polar angle and an azimuthal angle, all relative to a center of point cloud data 306).

The point cloud data obtained at block 205 can be stored in any of a variety of data structures, including, for example, a table containing a plurality of records, each corresponding to one point 308 and containing the colour data and position data for that point. A variety of other data structures will also occur to those skilled in the art.

The manner in which point cloud data 306 is obtained at block 205 is not particularly limited. As noted earlier, point cloud data can be generated by generation device 104 via the execution of animation application 135, in which case obtaining point cloud data 306 can include retrieving the point cloud data from memory 120. In other embodiments, in which capture volume 304 is a volume of real space (rather than a virtual volume generation via application 135), obtaining point cloud data at block 205 includes receiving and processing data from capture apparatus 134. A description of capture apparatus 134 itself follows, with reference to FIG. 4.

Capture apparatus 134 includes a plurality of capture nodes arranged in or around capture volume 304. Each node, placed in a distinct position from the other nodes, generates colour and depth data for a plurality of points in its field of view. In the present example, the field of view for each node is about three hundred and sixty degrees by about three hundred sixty degrees (that is, each node captures data in a full sphere). However, in other embodiments nodes may have reduced fields of view. The nature of the nodes is not particularly limited. For example, each node can include a camera and a depth sensor (e.g. a lidar sensor). In some embodiments, each node may include a plurality of cameras and depth sensors to achieve the above-mentioned field of view. An example of a device that may be employed for each node is the Bublcam by Bubl Technology Inc. of Toronto, Canada.

A wide variety of node arrangements may be employed to capture the raw data to be processed by generation device 104 in order to obtain point cloud data 306 at block 205. In general, greater numbers of nodes allow for a greater level of detail to be captured, particularly in complex scenes. Examples of presently preferred configurations of nodes for capture apparatus 134 are discussed below.

FIG. 4 illustrates three non-limiting examples of multi-node capture apparatuses 134, indicated as 134 a, 134 b and 134 c. Setup 500 has a tetrahedral shape, setup 504 has the shape of a triangular prism, and setup 508 has an octahedral shape. The capture volume 304 is also illustrated as a dashed-line sphere around each arrangement (although the actual size of capture volume 304 may be larger or smaller than shown in relation to apparatuses 134 a, 134 b, 134 c). Each arrangement includes a plurality of capture nodes including a central node x and peripheral nodes a, b, c, d, as well as (for apparatuses 134 b and 134 c) e and f.

The arrangements of capture apparatus 134 illustrated in FIG. 4 create safe movement zones within capture volume 304. A safe movement zone describes a volume around the center of capture volume 304 (i.e. the location of nodes x in FIG. 4) within which the resulting point cloud data 306 maintains continuity with capture volume 304. In other words, virtual reality display 156 will be able to simulate movement of the operator within this safe zone with substantially all rotations and positions in the volume supported. Conversely, outside of the safe movement zone, the likelihood of objects in capture volume 304 being incompletely captured in point cloud data 306 (because the objects are visible by too few nodes) increases.

Returning briefly to FIG. 2, at block 205 the process of obtaining point cloud data can therefore include receiving the point cloud data from capture apparatus 134. When (as shown in FIG. 4) capture apparatus 134 includes a plurality of nodes, generation device 104 can be configured to receive point cloud data 306 in a form that requires no further processing. In other embodiments, generation device 104 can receive raw data in the form of a plurality of point clouds from capture apparatus 134, and process the raw data to generate point cloud data 306, as discussed below in connection with FIG. 5.

FIG. 5 depicts a method 500 of generating point cloud data (e.g. as part of the performance of block 205 of method 200). At block 505, generation device 104 is configured to receive raw point cloud data from each node in capture apparatus 134. As will be apparent to those skilled in the art from FIG. 4, each node in any given capture setup can generate point cloud data for at least a portion of capture volume 304.

At block 510, generation device 104 is configured to register the raw point cloud data received at block 505 to a common frame of reference (i.e. the same coordinate space). For example, each node of capture apparatus 134 can be configured to generate point cloud data in which each point has coordinates (either Cartesian or spherical, as mentioned earlier) centered on the node itself. With the relative locations of the nodes being known, the point cloud data from any given node can be transformed via conventional techniques to a frame of reference centered on the center of capture volume 304.

It will now be apparent that when the sets of raw point cloud data are registered to a common frame of reference, a number of locations within capture volume 304 may be represented multiple times within the co-registered point cloud data. That is, more than one node may capture the same location in capture volume 304. Generation device 104 is therefore configured to collapse fully or partially any overlapping points in the co-registered point cloud data to a smaller number of points, as discussed below.

At block 515 generation device 104 is configured to determine, for each point in the co-registered point cloud data, whether the point overlaps (either exactly or partially) with other points in the common frame of reference. When the determination is negative, generation device 104 proceeds to block 520, at which the co-registered point cloud data is updated with no change being made to the non-overlapping points (in other words, the update may be a null update). When the determination at block 515 is affirmative for any points, however, generation device 104 can be configured to perform block 525. At block 525, generation device 104 is configured to determine whether the difference in colour between the overlapping points identified at block 515 is greater than a predetermined threshold. That is, if different nodes record significantly different appearances for the same location in capture volume 304, that is an indication that the capture volume includes surfaces that are highly reflective, specular or the like.

When the determination at block 525 is negative (e.g. the differences in colour for overlapping points are non-existent or below the above-mentioned threshold), generation device 104 proceeds to block 520 and updates the co-registered point cloud by replacing the overlapping points with a single point. The single point can have a colour value equivalent to an average of the colour values of the original overlapping points, for example.

When the determination at block 525 is affirmative, however, generation device 104 can be configured to create a palette image containing a subset, or all, of the colour values from the overlapping points. A palette image stores a plurality of possible colours for a single point in the co-registered point cloud. The palette image preferably stores possible colours in a two-dimensional array. The colour at the center of the palette image corresponds to the colour of the point when viewed from the center of the point cloud, and colours spaced apart from the center of the palette image in varying directions and at varying distances correspond to the colour of the point when viewed from corresponding directions and distances from the center of the point cloud. In some embodiments, rather than full colour values, the palette image can store only luminance or intensity values, while chrominance or other colour values can be stored in the point itself (along with a reference to the palette image).

At block 520, generation device 104 is then configured to update the co-registered point cloud with an index value pointing to the palette image (which can be stored separately from point cloud data 306), in place of a colour value. In some embodiments, the performance of blocks 525 and 530 can be omitted.

Returning to FIG. 2, once generation device 104 has obtained point cloud data 306, generation device 104 is configured to perform block 210 of method 200. At block 210, generation device 104 is configured to generate primary image data. The primary image data includes two components: (i) a projection of a first subset of the points defined in point cloud data 306 into a two-dimensional frame of reference (from the three-dimensional frame of reference of point cloud data 306); and (ii) for each point of the above-mentioned subset, depth data derived from the corresponding position data (in point cloud data 306) for that point.

In brief, the primary image data generated at block 210 depicts the portions of point cloud data 306 that are visible from a predicted viewpoint of virtual reality display 156. In other words, the primary image data depicts the portions of point cloud data 306 that are expected to be initially visible to the operator of virtual reality display 156. As will now be apparent, from any given viewpoint within point cloud data 306, any object may be occluded by other objects or by the object itself (e.g. the rear surface of an object may be occluded from view by the remainder of that same object). The above-mentioned subset of points in the primary image data correspond to the portions of point cloud data 306 that are visible from the initial viewpoint. Other points in point cloud data 306 that are not visible from the initial viewpoint are not included in the subset.

In general, generation device 104 is configured to generate the primary image data by selecting the above-mentioned subset of points, and for each of the subset of points, determining a projected location in a two-dimensional frame of reference for that point, along with accompanying depth data. An example implementation of block 210 will be discussed below, following the discussion of block 215.

At block 215, generation device 104 is configured to generate secondary image data. The secondary image data includes a projection (distinct from the projection mentioned above in connection with the primary image data) of a second subset of the points in point cloud data 306 into the two-dimensional frame of reference mentioned above. The second subset of points is distinct from the subset of points represented by the primary image data. More specifically, the second subset of points, when projected into the two-dimensional frame of reference, overlaps with at least part of the projection in the primary image data. That is, each of the second subset of points, when projected, occupies a location in the two-dimensional frame of reference that matches the location (in that same frame of reference) of a point in the first subset. The secondary image data also includes, for each point of the second subset, depth data derived from the corresponding position data of that point in point cloud data 306.

In contrast to the primary image data, the secondary image data depicts the portions of point cloud data 306 that are not visible from a predicted initial viewpoint established by virtual reality display 156. Instead, the secondary image data depicts portions of point cloud data 306 that are initially occluded by the primary image data, but may become visible due to movement of the viewpoint through manipulation of virtual reality display 156 by an operator.

As with the primary image data, generation device 104 is configured to generate the secondary image data by selecting the above-mentioned second subset of points, and for each of the second subset of points, determining a projected location in a two-dimensional frame of reference for that point, along with accompanying depth data. In the present example, generation device 104 is configured to perform blocks 210 and 215 in parallel (that is, substantially simultaneously) according to the process depicted in FIG. 6.

Referring now to FIG. 6, a method 600 of generating primary and secondary image data at generation device 104 (i.e. a method of performing blocks 210 and 215 of method 200) is depicted. Beginning at block 605, generation device 104 is configured to select a viewpoint within the volume depicted by point cloud data 306 (in other words, within capture volume 304). The selection of a viewpoint is the predicted starting location of the viewer, as detected by the virtual reality display 156. For example, the centre of point cloud data 306 may be selected as the viewpoint.

At block 610, generation device 104 is configured to select a vector (also referred to as a path) for processing. In the example above, in which point cloud data 306 defines a spherical volume (i.e. defined by spherical coordinates), the selection of a vector at block 610 comprises selecting azimuthal and polar angles. In general, at block 610 generation device 104 selects a path extending from the viewpoint selected at block 605, but does not select a depth (e.g. a radial distance when using spherical coordinates) corresponding to that path.

At block 615, generation device 104 is configured to identify the first point in point cloud data 306 that is visible to the selected viewpoint along the selected path or vector. That is, travelling along the selected path from the selected viewpoint, the first point in point cloud data 306 that the selected path intersects is identified, and projected into a two-dimensional frame of reference. Projection at block 615 includes determining two-dimensional coordinates, such as an x and a y coordinate, corresponding to the first visible point in a previously selected two-dimensional frame of reference. The projection can also include determining a depth for the first visible point, which defines the distance (generally in scalar form) from the viewpoint to the first visible point.

A wide variety of two-dimensional frames of reference may be employed at block 615. In the present example, the two-dimensional frame of reference is a cube map. Various features of cube maps, and various techniques for projecting points in three-dimensional space onto two-dimensional faces of cube maps, will be familiar to those skilled in the art. To illustrate the application of cube mapping to the present disclosure, reference is now made to FIG. 7A.

FIG. 7A depicts a viewpoint 700 centered within a cube 704 having six faces: an upper face 708, a lower face 712, a right face 716, a left face 720, a front face 724 and a rear face 728. In general, determining two-dimensional coordinates corresponding to a point 732 in three-dimensional space involves projecting point 732 towards viewpoint 700 until the path of projection intersects with one of the faces of cube 704 (in the example shown in FIG. 7A, the projection path intersects with right face 716). The location (defined by a horizontal coordinate and a vertical coordinate, e.g. x and y) of the intersection is the two-dimensional projection of point 732. Thus, any number of points in three-dimensional space can be represented on a two-dimensional plane, in the form of one of the faces of cube 704.

Referring now to FIG. 7B, an example of cube map projection as applied to point cloud data 306 is illustrated. In particular, a path 736 selected at block 610 is shown extending from a viewpoint (selected at block 605) centered on a cube. The first point in point cloud data 306 that is intersected by path 736 is point 308 a. The two-dimensional coordinates of the projection of point 308 a are the coordinates on the face of the cube intersected by path 736 during its travel from the viewpoint to point 308 a. Generation device 104 is also configured to determine the length of path 736 between the viewpoint and point 308 a, based on the positions in three dimensional space of the viewpoint and point 308 a. The length of path 736 represents a depth value corresponding to the two-dimensional projection of point 308 a.

Returning to FIG. 6, at block 620 generation device 104 is configured to determine whether any additional points intersect with the path selected at block 610 (that is, after the point projected at block 615). Referring again to FIG. 7B, path 736 intersects only one point (point 308 a). However, another path 740 intersects a point 308 b on one face of object 300 before traversing object 300 and intersecting another point 308 c on another face of object 300. Thus, for path 736 the determination at block 620 would be negative, but for path 740 the determination would be affirmative. Such additional points are also referred to as “fold” points, and generally represent locations in point cloud data 306 that require movement of the initial viewpoint in order to become visible.

When the determination at block 620 is affirmative, generation device 104 is configured to determine two-dimensional coordinates and depth data for any additional points along the selected path at block 625. As will now be apparent, the two-dimensional coordinates for the additional points are identical to those of the first visible point, and thus there is no need to repeat projection calculations at block 625. Instead, only the depth of such additional points needs to be determined.

At block 630, generation device 104 is configured to determine whether any additional paths remain to be processed. Generation device 104 is configured to process a plurality of paths to generate the primary and secondary image data. The number of paths to be processed is set based on the desired resolution of the primary and secondary image data—a greater number of paths (i.e. a higher-resolution sampling of point cloud data 306) leads to higher resolution image data. When paths remain to be processed, the performance of method 600 returns to block 610 to select the next path. When all paths have been processed, the performance of method 600 instead proceeds to block 635.

At block 635, generation device 104 is configured to store the first visible point projections and corresponding depth values as primary image data, and at block 640, generation device 104 is configured to store the additional point projections and corresponding depth values as secondary image data. Blocks 635 and 640 need not be performed separately after a negative determination at block 630. Instead, the storage operations at blocks 635 and 640 can be integrated with blocks 615 and 625, respectively.

The storage operations of blocks 635 and 640 will be described in greater detail in conjunction with FIGS. 8 and 9A-9B. Referring now to FIG. 8, an example of primary image data is shown in the form of two packages of data 800 and 804, such as image files. Although the term “file” is used herein to discuss image data stored in packages 800 and 804 as well as other packages to be introduced, the files discussed herein can be stored in other types of packages, including streams of data, blocks of memory in a CPU or GPU, and the like. File 800 contains the colour data for the primary image data, and file 804 contains the depth data for the primary image data. Each file is divided into regions corresponding to faces of cube 704, described above. The regions of files 800 and 804 are arranged to represent the unfolding of cube 704 into a cross shape, and the relocation of rear face 728 and lower face 712 to transform the cross shape into a rectangular shape that corresponds more closely with conventional image formats. Any arrangement of the faces of cube 704 can be employed in files 800 and 804, however. In general, files 800 and 804 use the same arrangement of faces; in some embodiments, however, different arrangements may be employed for each of files 800 and 804, the added requirement of storing data (for example, in an index or other metadata to be discussed below) defining the concordance between files 800 and 804.

Each of files 800 and 804 consists of a two-dimensional array. In the case of file 800, the two-dimensional array is an array of pixels, each storing colour data in any suitable format (e.g. HSV). Thus, as illustrated in FIG. 8, the regions corresponding to face 716 contain colour data and depth data for a subset of the points representing object 300 (specifically, the subset visible from viewpoint 700), while the remaining faces are blank (e.g. contain null values), as no other objects exist in the simplified example capture volume 304 discussed herein. Although faces 716 are shown populated with an image for illustrative purposes, files 800 and 804 are generally implemented with arrays of numeric values (e.g. triplets of values in each pixel of file 800, and a single depth value in each pixel of file 804). It is contemplated that the pixels of files 800 and 804 do not contain any positional data. Rather, such positional data is implicit in the position of the pixels in the above-mentioned two-dimensional array.

Turning to FIG. 9A, in some embodiments the secondary image data (that is, the fold points, or folds) can be stored in two files 900 and 904. File 900 contains colour data for each of the additional points detected and projected at blocks 620 and 625, while file 904 contains depth data for each of the additional points. In addition, files 900 and 904 preferably have the same dimensions as files 800 and 804 described above. As with files 800 and 804, files 900 and 904 include a plurality of pixels in a predefined two-dimensional array, with each pixel containing either a null value, or colour values (for file 900) or a depth value (for file 904). Files 900 and 904 are divided into the same regions as files 800 and 804 (corresponding to the faces of cube 704). This technique of storing secondary image data may also be referred to as regional fold data.

As seen in FIG. 9A, the region of files 900 and 904 corresponding to face 716 of cube 704 depicts a different portion of object 300 than files 800 and 804. Specifically, files 800 and 804 depict the “top” of object 300, which includes point 308 c, labelled in FIG. 7B. As discussed earlier, and as shown in FIG. 8, the top of object 300 is not visible in the primary image data. Instead, the top of object 300 is “behind” the portion of object 300 shown in files 800 and 804, from the perspective of viewpoint 700.

It will now be apparent that the “back” of object 300 is also not visible in the primary image data. In some examples, the back of object 300 would therefore also be depicted in files 900 and 904. In the present example, however for illustrative purposes, the back of object 300 has been omitted from files 900 and 904. More specifically, generation device 104 can be configured, at block 625, to determine whether a fold point is within a predicted range of motion of the viewpoint selected at block 605 before projecting the fold point. That is, generation device 104 can store a predicted maximum travel distance for viewpoint 700, and omit fold points entirely if such points would only become visible if the viewpoint moved beyond the maximum travel distance. In the presently preferred embodiment, however, such determinations are omitted from the generation of secondary image data, and instead addressed at the rendering stage, to be discussed further below.

In the example shown in FIGS. 7B and 9A, only one additional layer of points is present in point cloud data 306 behind the points of the primary image data. All fold points can therefore be readily represented in files 900 and 904 in their “true” locations. However, in more complex point cloud data, further fold points may be detected at blocks 620 and 625 behind other a first layer of fold points (in much the same way as the fold points shown in FIG. 9A lie “behind”, or overlap, the primary points shown in FIG. 8). In such embodiments, generation device 104 can create a further pair of files 800 and 804 for each deeper layer of fold points. Preferably, however, only a single pair of files 800 and 804 are employed by generation device 104 to store all fold data. Therefore, generation device 104 is configured to detect collisions between fold points—instances in which multiple fold points have the same two-dimensional projections. Generation device 104 is configured to store such colliding fold points in a manner described below in connection with FIGS. 10A and 10B.

FIG. 10A depicts viewpoint 700 and cube 704, with a path extending from right face 716 and intersecting with three points A, B and C in point cloud data 306. According to the process shown in FIG. 6, point A is stored as primary image data, and points B and C are stored as secondary image data. However, the two-dimensional projections of points B and C have the position, and thus the point collide in files 900 and 904. Generation device 104 is therefore configured, as shown in FIG. 10B, to store point B in a file 900′, in the actual position of the two-dimensional projection of all three points. Point C, meanwhile, is offset from point A in the two-dimensional array. In other words, generation device 104 is configured to detect collisions between fold points, and when a collision is detected, generation device 104 is configured to search the vicinity of the collision location for an unused pixel, and to store the colliding point in the unused pixel. Generation device 104 is also configured to store an offset for the colliding point (point C, in the present example). The offset can be stored in file 900 or 904 themselves (e.g. in a header or other metadata segment of the files, or in the UV—chrominance—portion of the relevant depth file, as depth is a single value and can thus be stored in the Y—luminance—portion of the file), or in a separate index file (e.g. containing the position of point C in file 900′, and an offset vector or coordinate pair indicating the true position of point C). Substantial portions of files 900 and 904 may be empty, depending on the complexity of the scene, and thus the above process may make more efficient use of storage space than generating a plurality of layers of files 900 and 904.

Returning to FIG. 9B, in other embodiments the secondary image data can be stored in files 908 and 912 rather than in files 900 and 904. Files 908 and 912 have different data structures than files 900 and 904, as will be discussed below. In the present embodiment, files 908 and 912 have a predetermined height “H”, but a variable length “L” (in contrast with files 800 and 804, as well as 900 and 904, which have predetermined height and length). In general, the length L is determined by the volume of data to be stored in files 908 and 912, which varies based on the number of additional points identified and projected at blocks 620 and 625. Neither H nor L need equal the height or length of files 800 and 804. File 908 contains colour data for each of the additional points detected and projected at blocks 620 and 625, while file 912 contains depth data for each of the additional points.

While files 900 and 904 do not contain explicit position data in the pixels thereof—since such position data is implicit in the pixel array—files 908 and 912 do contain such position data, indicating the position of the colour and depth values of files 908 and 912 within the array of files 800 and 804. This is because the dimensions of files 908 and 912 generally do not match those of files 800 and 804, and thus the position of a data point within file 908 or 912 may not imply a specific position in the array of files 800 and 804. Generation device 104 is configured to perform various processing activities to reduce the volume of position data stored in files 908 and 912.

In general, generation device 104 is configured to identify portions of the two-dimensional frame of reference (that is, the two-dimensional array according to which files 800, 804, 900 and 904 are formatted) that are occupied at least to a threshold fraction by fold points. For any such portions that are identified, generation device 104 is configured to select geometric parameters identifying the portion, and store the geometric parameters along with the colour or depth data for the fold points within the portion (absent individual positional data for each fold point) in files 908 and 912. In other words, generation device 104 is configured to group the fold points into portions such that the locations of those fold points within the two-dimensional array can be represented with a volume of data that does not exceed—and is preferably smaller than—the volume of data required to store the individual coordinates of each fold point.

Generation device 104 can be configured to identify portions of a variety of different types. For example, generation device 104 can be configured to identify any one of, or any combination of, straight lines, curved lines, polygons, circles and the like. Generation device 104 is configured to select a portion, determine the total number of available positions in the two-dimensional array that are contained by that portion, and determine whether at least a threshold fraction of the positions within the portion contain fold data. The threshold fraction can be preconfigured at generation device, or can be determined dynamically based on the selected portion. When the determination is negative (i.e. too few fold points are present within the portion), generation device 104 is configured to select and evaluate a different portion according to the above process. When the determination is affirmative, however, generation device 104 is configured to store geometric parameters corresponding to the portion, as well as colour data or depth data for each fold point within the portion, in files 908 and 912. Having stored the geometric parameters and corresponding colour and depth data, generation device 104 is configured to repeat the above process on the remaining fold points (that is, those not yet assigned to portions) until all fold point data has been stored.

Turning to FIG. 11, an example of the above process is illustrated. An array 1100 is shown having the dimensions of files 800 and 804, and divided into regions corresponding to the faces of cube 704. Face 716 contains fold points defining a polygon representing the top of object 300, as discussed above, while face 720 contains two fold points (whose size is exaggerated for illustrative purposes). The points in face 720 are not present in capture volume 304 or point cloud data 306, but rather are provided in this particular example to illustrate the process of storing secondary image data.

Generation device 104 may determine that a portion of face 720 in the shape of a line extending between the two points in face 720 encompasses both of those points. However, storing secondary image data for such a line, as indicated at 1100, requires storing geometric parameters such as a start location and an end location (e.g. the locations of the two fold points themselves), as well as colour (or depth) data for the entire line. As indicated by the darker-coloured points, only two colour or depth values in the line represent fold points. The remaining, light-coloured, points simply contain null values. Thus, the total storage requirements for the line are greater than simply storing the two points individually with location data for each point. In other words, generation device 104 may determine that the number of fold points on the line is below a threshold at which the volume of data required to store the line is lower than the volume of data required to store the individual points. Generation device 104 therefore does not store the line, and may instead select a different portion of face 720 to test.

Referring to face 716, on the other hand, generation device 104 may determine that a polygon having corners at the corners of the top of object 300 is entirely filled with fold point data. Thus, face 716 can be represented in files 908 and 912 by coordinates for the four corners, and a set of colour or depth data without explicitly specified position data. As will now be apparent, this requires less storage space than storing each individual point in the polygon along with its individual coordinates within the array.

As noted earlier, a variety of types of geometric structures are contemplated for storing fold points. These include x-folds, indicating horizontal lines extending across the entirety of either a face of the array or the entire array; y-folds, indicating vertical lines extending across the entirety of either a face of the array or the entire array; partial x- or y-folds, indicating horizontal and vertical lines, respectively, that extend only partially across a face or array and thus are represented by start and end point rather than a single x or y index value. The types of geometric structures also include curved lines (e.g. defined by start points, end points and radii), polygons (e.g. defined by coordinates of the corners of the polygons), and angled lines (e.g. defined by start and end points). Any points that cannot be assigned to portions more efficiently than storing the points individually (that is, any points for which the determinations above remain negative after all other fold data has been stored) can be stored as individual points, also referred to as m-folds.

Returning to FIG. 9B, therefore, files 908 and 912 may have various sections, distinguished from each other by header data or tags indicating the start or end of each section, with each section containing a certain type of fold. Thus, in the present example, files 908 and 912 each contain a single section including header data 916 and 920. Header data 916 corresponds to colour data 924, and header data 920 corresponds to depth data 928. The header data includes geometric parameters, such as the corners of the polygon shown in FIG. 9A, and may also contain an identifier of the type of fold that follows (e.g. a polygon rather than an x-fold or a y-fold).

Returning to FIG. 6, the storage of primary and secondary image data at blocks 635 and 640 may also include generating an index file. The index file can contain the offset values mentioned above in connection with FIG. 10B. The index file can also contain data identifying the relative positions of the primary and secondary image data. For example, when the secondary image data is stored in accordance with the structure shown in FIG. 9B, the index can contain one or more pairs indicating which locations in the frame of reference of files 800 and 804 correspond to which locations in files 908 and 912.

When the primary and secondary image data have been stored, generation device 104 proceeds to the next frame at block 645. As will now be apparent, the above process generates primary and secondary image data for a single set of point cloud data 306, which depicts a single frame (i.e. a still image or a frame of a video). Method 600 can therefore be repeated for a plurality of other frames when the virtual reality multimedia data includes video data.

Variations to the processes described above for storing primary and secondary image data are contemplated. For example, rather than selecting the first visible point (i.e. the “shallowest” point) at block 615, generation device can be configured to select the deepest point at block 615, and to detect additional points as those points that are in between the viewpoint and the primary point rather than behind the primary point. In further embodiments, other divisions of image data between the primary image data and the secondary image data can be implemented. For example, instead of dividing point cloud data 306 based on visibility to viewpoint 700 as described above, the primary and secondary image data can be selected based on a predetermined depth threshold. That is, points located at a depth (from viewpoint 700) greater than the threshold can be included in one of the primary and secondary image data, while points located at a depth smaller than the threshold are included in the other of the primary and secondary image data. When this implementation is used, both primary and secondary image data can be stored in structures similar to that shown in FIG. 9A and 10B. In other words, both colour and depth files for each of the primary and secondary image data can include offsets to manage point collisions. In further embodiments, the division of data between the primary and secondary image data can be based on any suitable combination of factors, including any one or more of surface flatness rather than depth (i.e. based on variations of depth in the area of the points).

Various other data structures are also contemplated for storing the primary and secondary image data. For example, files 800 and 804 can be subdivided into a plurality of files or other package types, each file corresponding to a single face of cube 704. In further embodiments, individual files may be generated by generation device 104 for each face of cube 704, but each file can contain both colour and depth data rather than colour and depth data being separated into distinct files. In such embodiments, the above-mentioned index can also include data defining the relative position of the face-specific files.

Further variations to the generation process are contemplated. For example, generation device 104 can be configured to employ depth files such as files 804 and 904 as intermediate files, not sent to client device 108 but rather employed to generate an index file. More specifically, generation device 104 can be configured to perform a method 1200, depicted in FIG. 12, for generating the index file mentioned above. It is contemplated that method 1200 can be performed for each of the primary and secondary image data. Beginning at block 1210, generation device 104 is configured to identify a portion of the primary or secondary image data (specifically, the depth data in files 804 or 904) to be discarded. For example, generation device 104 can compare each depth value to a predetermined threshold, to determine whether each depth value is above (i.e. further from viewpoint 700) or below (i.e. closer to viewpoint 700) the threshold. Other processes may also be employed for selecting a portion of the depth data. The depth threshold can be predetermined as an absolute value, or as a fraction (e.g. 80%) of the maximum depth present in the primary and secondary image data.

Having identified the above-mentioned portion, at block 1215 generation device 104 is configured to discard the identified depth values. The corresponding colour data for the identified points is retained, however. Thus, for certain points in files 800, 900 or 908, the corresponding depth values in files 804, 904 or 912, respectively, are discarded. FIGS. 13A and 13B illustrate the effect of the performance of block 1215. FIG. 13A depicts a viewpoint 1300, assumed to be facing towards three cylinders 1302, 1304 and 1308 represented by primary and secondary image data generated at generation device 104. The depth data corresponding to cylinders 1304 and 1308 is beyond a depth threshold applied at block 1210, and thus generation device 104 is configured to discard the depth data associated with the points representing cylinders 1304 and 1308. As a result, the primary and secondary image data retained for further processing following the performance of block 1215 is illustrated in FIG. 13B, in which cylinders 1304 and 1308 are represented simply as flattened cylinders (e.g. rectangles) 1312 and 1316 on a background plane 1320, which may for example be at infinite depth.

Returning to FIG. 12, at block 1220, generation device 104 is configured to select an index of the retained depth data (i.e. depth data not discarded at block 1215). More specifically, turning to FIG. 14, generation device 104 is configured to generate an index file 1400 to replace depth files 804 or 904. Index file 1400 is illustrated in FIG. 14 as having the same dimensions as file 800 (also shown in FIG. 14 for illustrative purposes), although in practice file 1400 can have any suitable dimensions. Index file 1400 includes a plurality of subregions 1404, each corresponding to an equivalent subregion of file 800. In each subregion 1404, generation device 104 is configured to store a list of remaining depth values, in conjunction with a subregion index indicating the position of the depth values in a corresponding subregion of file 800. In other words, a plurality of triplets (d, x, y) are stored in subregions 1404. The size—and therefore the number—of subregions 1404 can be selected, for example, based on the bit depth of the indices x and y used to indicate locations within each subregion. For example, an 8-bit index permits the identification of a 256×256 grid, and thus subregions 1404 should not exceed 256 pixels in height or width. As will be seen below, client device 108 also employs the same subregions.

Thus, through method 1200, generation device 104 replaces depth files (such as file 804) with an index of a subset of the depth values in the original depth files. The index can additionally identify individual points as well as geometric parameters encompassing a plurality of points. That is, each subregion 1404 can include a plurality of index lists, each list containing depth and position data for a different type of geometry (e.g. different point sizes including both small, or single-pixel points, and large, or multi-pixel points, background polygons such as rectangles, other polygons such as triangles, and the like). For example, each subregion 1404 of index 1400 can include a background plane corresponding to the equivalent portion of plane 1320 shown in FIG. 13B.

Returning to FIG. 2, having generated primary and secondary image data at blocks 210 and 215, generation device 104 is configured to transmit the primary and secondary image data to client device 108, for example via network 112, at block 220. Prior to the transmission of the image data, generation device 108 can perform various preprocessing techniques to prepare the data for transmission. For example, conventional compression algorithms for two-dimensional images and video streams can be applied to reduce the volume of data to be transmitted. In the present example, the primary and secondary image data are formatted into streams of data and compressed according to any suitable standard, such as H.264, VP8/VP9 and the like. The streams of data (or any other suitable packaging for the data) can be formatted according to any suitable container format, including that specified by the Motion Pictures Expert Group (MPEG)-4 standard.

In addition, generation device 104 can be configured to create additional versions of the primary and secondary image data having lower resolutions than the original versions. For example, generation device 104 can receive an indication from client device 108 of the location and direction of viewpoint 700, and transmit virtual reality multimedia data that includes either down sampled versions or omits entirely the portions of the primary and secondary image data that is not currently visible from the viewpoint location and direction. For example, image data for one face of cube 704 may be transmitted at an original resolution, while the other faces may be transmitted at a lower resolution, or simply omitted. Combinations of the above are also contemplated.

At block 225, client device 108 is configured to receive the data transmitted by generation device 104 (or an intermediary, as noted earlier), and decode the prepared data, based on the standard according to which the data was encoded for transmission at block 220 (e.g. MPEG4). In other words, at block 225 client device 108 is configured to retrieve, from the data received from generation device 104, the primary and secondary image data described above, in the form of files 800 and 804, as well as files 900 and 904 or files 908 and 912 (or variants thereof). Alternatively, client device 108 can receive the above-mentioned index files as discussed in connection with FIG. 14, rather than depth files 804, 904 or 912.

At block 230, client device 108 is configured to receive a viewpoint position and direction from virtual reality display 156. The position and direction received at block 230 need not match the position of viewpoint 700 discussed above. Viewpoint 700 was employed for projecting point cloud data 306 into two dimensions, and reprojecting the primary and secondary image data into three dimensions to recreate point cloud data 306. The position and direction received at block 230, on the other hand, corresponds to the position and direction of the viewpoint within point cloud data 306 as detected by virtual reality display 156 under the command of an operator. The position and direction of the viewpoint may be detected by way of accelerometers, pupil detection cameras, or any other suitable sensors included in virtual reality display 156.

Upon receipt of the viewpoint position and direction, at block 235 client device 108 is configured to select and render at least a portion of the primary and secondary image data received at block 225, based on the viewpoint position and direction received at block 230. In general, the selection and rendering process includes selecting data from the primary and secondary image data at the CPU of client device 108, and issuing one or more draw calls to a GPU, for causing the GPU to regenerate point cloud data based on the selected image data and control virtual reality display 156. As will be discussed below, client device 108 is configured to implement various processing techniques to reduce the volume of point cloud data to be regenerated and processed to control virtual reality display 156 (i.e. to reduce the computational load on the GPU).

Client device 108 is configured to select a subset of the primary and secondary image data received at block 225, based on the viewpoint position and direction (including a definition of the field of view of the viewpoint, also referred to as the frustum of the viewpoint) received at block 230. For example, client device 108 can be configured to determine which face, or combination of faces of cube 704 are visible based on the viewpoint position. Generally, three or fewer faces will be visible from the viewpoint. Client device 108 can therefore be configured to omit from further processing any primary and secondary image data located on the faces that are not visible to the viewpoint. For example, if the viewpoint has the same location as shown in FIG. 7B, and is directed towards face 716, then client device 108 may determine that face 716 is the only face that is currently visible to the viewpoint. The other five faces may therefore be omitted from further processing. In other words, the primary image data of files 800 and 804 corresponding to the faces other than face 716, and the secondary image data of files 900 and 904 or files 908 and 912 corresponding to the faces other than face 716, may be omitted.

In further embodiments, referring to FIG. 13, client device 108 can be configured to subdivide each face of the two-dimensional array into a plurality of subregions corresponding to those discussed in connection with FIG. 14. Client device 108 can therefore be configured to select a subset of subregions 1404 that are impinged by the field of view and omit all other subregions.

Following the selection of primary and secondary image data for rendering, client device 108 is configured to transmit the selected colour and depth data for rendering. For example, the CPU of client device 108 can be configured to generate a plurality of draw calls and transmit the draw calls to the GPU of client device 108, or to a GPU or other processor integrated with virtual reality display 156. Response to receiving such data, the GPU (or any other suitable processor connected to virtual reality display 156) is configured to regenerate point cloud data from the selected colour and depth data, and present the regenerated point cloud data at virtual reality display 156.

The data transmitted to the GPU or any other suitable processing hardware at block 1225 can include one or more indices of points or geometries, according to the format of data received from generation device 104. For example, when indices such as those described in connection with FIG. 14 are received from generation device 104, client device 108 is configured to submit different types of draw calls based on the type of geometry listed in the index. For example, as noted earlier the index received from generation device 104 can include different point sizes.. The data sent to the GPU can therefore instruct the GPU to draw a large point, which causes the GPU to render a larger point to fill in the space between the non-adjacent points provided in the indices. In addition, the colour of the large point can be selected based on colour data for a plurality of points surrounding the center of the large point.

It is contemplated that blocks 230 and 235 are generally performed twice in parallel. Virtual reality display 156 generally includes two distinct displays (corresponding to the eyes of the operator), and thus at block 230 includes receiving two viewpoint positions and block 235 includes selecting and rendering two distinct sets of image data. Having rendered image data at block 235, client device 108 is configured to return to block 230 to receive updated viewpoint positions. In some embodiments, the viewpoint positions can be transmitted to generation device 104, which can perform at least some of the selection activities referred to above, and send the resulting image data to client device 108.

Variations to the above systems and processes are contemplated. For example, rather than capturing, processing and rendering a scene (e.g. capture volume 304) in order to simulate movement of the operator of virtual reality display 156 within the scene, system 100 can also be configured to capture, process and render an object in order to simulate movement of the operator of virtual reality display 156 around the object. Capturing the object to generate point cloud data can be accomplished substantially as described above, however central nodes (e.g. node “x” in FIG. 4) are generally omitted, as the object to be captured is generally in that location.

In further variations, rendering computational performance (e.g. at block 235) may be improved by reducing the resolution of the rendered image data based on the proximity of the image data to the center of the viewpoint frustum. For example, image data determined by client device 108 to be near the outer edge of the viewpoint frustum can be reduced in resolution. In an example embodiment, the reduction in resolution can be achieved by replacing a number of small points with a small number of large points, prior to transmission of image data and geometric parameters to the GPU for rendering. In implementations employing the subdivisions shown in FIG. 13, client device 108 can determine whether a subregion 1300 is a peripheral subregion (i.e. located at the periphery of the viewpoint frustum), and for peripheral subregions can reduce the resolution prior to data transmission to the GPU.

It is also contemplated that the source of the image data described herein can be supplemented or replaced with light field capture data (e.g. obtained from one or more light field cameras in capture apparatus 134). Light field data represents a collection of light rays passing through a volume. Such data can indicate not only position and colour data for a plurality of points, but also properties such as the incident direction of light on the points and the appearance of each point from a plurality of different directions. In some embodiments, the light field data can omit depth data. However, the depth data can be determined from the depth data.

The scope of the claims should not be limited by the embodiments set forth in the above examples, but should be given the broadest interpretation consistent with the description as a whole. 

1. A method of generating virtual reality multimedia data, comprising: obtaining point cloud data at a processor of a generation computing device, the point cloud data including colour and three-dimensional position data for each of a plurality of points corresponding to locations in a capture volume; generating, at the processor, primary image data containing (i) a first projection of a first subset of the points into a two-dimensional frame of reference, and (ii) for each point of the first subset, depth data derived from the corresponding position data; generating, at the processor, secondary image data containing (i) a second projection of a second subset of the points into the two-dimensional frame of reference, the second projection overlapping with at least part of the first projection in the two-dimensional frame of reference, and (ii) for each point of the second subset, depth data derived from the corresponding position data; and storing the primary image data and the secondary image data in a memory connected to the processor.
 2. The method of claim 1, wherein obtaining the point cloud data includes retrieving the point cloud data from a memory.
 3. The method of claim 1, wherein obtaining the point cloud data includes: receiving raw point cloud data from a capture apparatus; and generating the point cloud data by registering the raw point cloud data to a common three-dimensional frame of reference.
 4. The method of claim 1, the primary image data including: a first image dimensioned according to the two-dimensional frame of reference and containing colour data for each point of the first subset; and a second image dimensioned according to the two-dimensional frame of reference and containing depth data for each point of the first subset.
 5. The method of claim 4, wherein the first image and the second image are cube map projections.
 6. The method of claim 4, wherein the first image and the second image are YUV images having luminance and chrominance channels, and wherein the depth data includes a depth value stored in the luminance channel.
 7. The method of claim 1, the secondary image data including: a first image dimensioned according to the two-dimensional frame of reference and containing colour data for each point of the second subset; and a second image dimensioned according to the two-dimensional frame of reference and containing depth data for each point of the first subset.
 8. The method of claim 1, wherein the first image and the second image are cube map projections.
 9. The method of claim 7, further comprising: detecting that a plurality of colliding ones of the second subset of points have a common position in the two-dimensional frame of reference; storing colour data and depth data for one of the colliding points in the first image and the second image according to the common position; storing colour data and depth data for another of the colliding points in the first image and the second image at a two-dimensional offset from the common position.
 10. The method of claim 9, further comprising: storing the two-dimensional offset in the second image.
 11. The method of claim 1, wherein generating the primary image data includes: setting a viewpoint position corresponding to a location in the capture volume; and selecting the first subset of the points by: for each of a plurality of paths extending from the viewpoint position, selecting the first point of the point cloud data encountered by the path.
 12. The method of claim 1, wherein generating the primary image data includes: setting a viewpoint position corresponding to a location in the capture volume; and selecting the first subset of the points by: determining a distance from the viewpoint to each of the plurality of points; comparing the distance to a threshold; and selecting the points having a smaller distance than the threshold from the viewpoint.
 13. The method of claim 1, further comprising: transmitting the primary image data and the secondary image data for receipt by a client device.
 14. A generation computing device, comprising: a memory; a network interface; and a processor interconnected with the memory and the network interface, the processor configured to: obtain point cloud data at a processor of a generation computing device, the point cloud data including colour and three-dimensional position data for each of a plurality of points corresponding to locations in a capture volume; generate primary image data containing (i) a first projection of a first subset of the points into a two-dimensional frame of reference, and (ii) for each point of the first subset, depth data derived from the corresponding position data; generate secondary image data containing (i) a second projection of a second subset of the points into the two-dimensional frame of reference, the second projection overlapping with at least part of the first projection in the two-dimensional frame of reference, and (ii) for each point of the second subset, depth data derived from the corresponding position data; and store the primary image data and the secondary image data in the memory.
 15. A method of rendering virtual reality multimedia data, comprising: obtaining primary image data containing (i) a first projection of a first subset of points in a three-dimensional point cloud into a two-dimensional frame of reference, and (ii) for each point of the first subset, depth data derived from corresponding position data of the points; obtaining secondary image data containing (i) a second projection of a second subset of the points into the two-dimensional frame of reference, the second projection overlapping with at least part of the first projection in the two-dimensional frame of reference, and (ii) for each point of the second subset, depth data derived from the corresponding position data; receiving a viewpoint position from a virtual reality display; selecting at least a portion of the primary image data and the secondary image data based on the viewpoint position; and rendering the selected primary and secondary image data on the virtual reality display.
 16. A client computing device, comprising: a memory; a network interface; and a processor interconnected with the memory and the network interface, the processor configured to: obtain primary image data containing (i) a first projection of a first subset of points in a three-dimensional point cloud into a two-dimensional frame of reference, and (ii) for each point of the first subset, depth data derived from corresponding position data of the points; obtain secondary image data containing (i) a second projection of a second subset of the points into the two-dimensional frame of reference, the second projection overlapping with at least part of the first projection in the two-dimensional frame of reference, and (ii) for each point of the second subset, depth data derived from the corresponding position data; receive a viewpoint position from a virtual reality display; select at least a portion of the primary image data and the secondary image data based on the viewpoint position; and render the selected primary and secondary image data on the virtual reality display. 